Hair care appliances have been available, which hold and heat a hair curler or set of hair curlers for hairdressers' or consumers' own personal use in curling hair. Many such appliances have no indicators indicating whether their heaters are on or off, and most provide no indication to the user as to curler temperature or when the curlers are ready for use. Some appliances have a power-on indicator, and some have a "ready light." The temperature of the curlers is an important factor in curling hair, particularly with respect to retention of curl by the hair after curling, as described in more detail below. Thus there is a need for hair curlers and appliances which indicate to the user at a glance, whether the heaters are operating during the heating phase. There is also a need for curlers which indicate accurately when each curler is at a temperature that provides the best hair curling results, especially in retention of curl. There is also a need for curlers which indicate to the user when the curling process is complete, so that curlers are not left in place in the hair for a longer time than necessary. Since temperature can vary from one portion of a curler to another, there is a need for the temperature indication to refer to the actual surface around which the hair is curled. Materials with specific properties are required. New processes are needed for preparing such materials and using them in manufacture of curlers.